The magnetoresistance (MR) effect is a phenomenon in which the electrical resistance is changed by application of a magnetic field to a ferromagnetic material, and used for the magnetic field detector and the magnetic head. In recent years, an artificial lattice film such as Fe/Cr, Co/Cu has been come to be known as a giant magnetoresistance (GMR) effect material exhibiting a very large magnetoresistance effect.
Also, what is called a spin valve film having a structure including a ferromagnetic layer, a nonmagnetic layer, a ferromagnetic layer and an antiferromagnetic layer is known, in which the nonmagnetic metal layer has such a thickness as to substantially eliminate the switched connection function between the ferromagnetic layers, and in which the magnetic moment of the ferromagnetic layer adjacent to the antiferromagnetic layer is fixed as what is called a fixed layer by the switched connection between the particular ferromagnetic layer and the antiferromagnetic layer while only the spin of the other ferromagnetic layer constitutes a free layer easily inverted by an external magnetic field. The antiferromagnetic material is formed of FeMn, IrMn, PtMn or the like. In this case, the switched connection between the two ferromagnetic layers is so weak that the spin can be inverted in a weak, small magnetic field. Thus, a highly sensitive magnetoresistive element can be provided and used as a high-density magnetic recording and read head. The spin valve film described above is used by supplying a current inward of the film surface.
On the other hand, it is known that a still larger magnetoresistance effect can be produced utilizing the vertical magnetoresistance effect for supplying a current in the direction perpendicular to the film surface.
Further, a tunneling magnetoresistance (TMR) effect due to the ferromagnetic tunnel coupling is known which utilizes the fact that the magnitude of the tunneling current in the direction perpendicular to the film surface is differentiated by arranging the spins of the two ferromagnetic layers in parallel or antiparallel to each other with an external magnetic field in a three-layer film of a ferromagnetic film, an insulating film and a ferromagnetic film.
In recent years, the use of the GMR or TMR element as a magnetic field detector has also been studied. In this connection, the magnetoresistive element of pseudo spin valve type with a nonmagnetic metal layer sandwiched by two ferromagnetic layers of different coercive forces and the magnetoresistive element of spin valve type described above are studied. In an application as a magnetic detector, the resistance value is changed by changing the relative angles of these two ferromagnetic layers making up each element in response to an external magnetic field. This change in resistance value is detected by reading a voltage change signal while supplying a constant current. The reading process is executed using the GMR or TMR effect.
The magnetoresistance change of the GMR element is smaller than that of the TMR element, and in order to obtain a large change rate, a stack structure of repetitive sets of a ferromagnetic layer and a nonmagnetic layer is required. Also, the GMR element, in which a current is supplied in the direction perpendicular to the film surface, is not required to be lengthened. Since the GMR element is smaller in resistance than the TMR element, however, the current amount is required to be increased to produce a large output signal. As a result, the power consumption is increased. Further, in the GMR element in which the current is supplied in the direction inward of the film surface as described above, a sufficient current path is required in the element and therefore the length of the element is required to be increased in order to produce a large magnetoresistance effect.
For the reason described above, the magnetic field detector desirably uses the TMR element which can produce a large output signal and can be provided in an arbitrary shape.
Further, a technique has been proposed in which a single magnetoresistive element is not used for measurement, but a bridge circuit is formed using four magnetoresistive elements, and elements with the fixed layers having opposite directions of magnetization are combined to form a high-output magnetic field detector (see Japanese Patent No. 3017061).
Patent Document 1: Japanese Patent No. 3017061